Regulators of G protein signaling (RGS) are a family of proteins known to play a critical role in modulating the signaling of G protein-coupled receptors (GPCRs). Through interaction of their characteristic RGS domains with activated G-alpha subunits, RGS proteins accelerate GTP hydrolysis to attenuate downstream signaling. Our lab has recently demonstrated the first evidence that RGS proteins can also interact directly and selectively with the intracellular third loop of a number of GPCRs, yet the functional significance of this interaction has yet to be determined. The studies proposed in this application will examine the consequences of this RGS/GPCR interaction using RGS2 and the M1 muscarinic acetylcholine receptor (M1 AChR) as a model functional pair. Studies will include determining the sites of interaction on both RGS2 and M1 AChRs, examining the effects of the interaction on the binding of other regulatory proteins (i.e. GRKs and arrestins), and its functional effects on both G protein signaling and M1 AChR desensitization and internalization. Understanding the molecular interactions and functional significance of RGS/GPCR interactions will be critical in advancing our understanding of GPCR signaling and regulation in general. [unreadable] [unreadable]